According to an analysis by Citigroup, initial feedback following the accusations against GSK and investigations into other firms suggested that Chinese sales at Britain's biggest drug maker were down as much as 30pc or more in volume terms since June.

Industry insiders say GSK is facing heightened barriers to business in China amid the bribery scandal, with major hospitals refusing entry to sales representatives. While other multinational pharmaceutical companies have also been blocked, GSK's sales are thought to have suffered the worst.

GSK has declined to quantify its expected sales loss but admitted in its second quarter results that there would be "some impact to our performance in China".

In July, four of the company's Chinese sales executives were arrested for allegedly funnelling up to £320m in bribes to doctors and officials to clinch higher prices and win market share .

Such is the pressure on the British drug maker, that it is mulling a complete withdrawal from the market, according to sources close to the company. However, some industry experts doubt that the drug maker would go through with an exit from one of the world's fastest-growing pharmaceuticals markets and a GSK spokesman said the company remains "fully committed to China and to continuing to supply our healthcare products to meet the needs of patients in the country.”

While GSK only generates around 3.6pc of its revenues in China, sales in the country have grown at a double-digit pace in recent years.

Chinese authorities have since launched an investigation into Sanofi, which is alleged to have bribed more than 500 Chinese doctors with Rmb1.7m in late 2007, to raise sales. The French drug maker said it took the accusations “very seriously” and has “zero tolerance” towards unethical practice.